1. Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to a system and method for providing compatibility between phase controlled dimmers and lighting systems.
2. Description of the Related Art
Dimming a light source saves energy and also allows a user to adjust the intensity of the light source to a desired level. Many facilities, such as homes and buildings, include light source dimming circuits (referred to herein as “dimmers”). Power control systems with switching power converters are used to control light sources, such as discharge-type lamps. Discharge lamps include gas discharge lamps such as, fluorescent lamps, and high intensity discharge lamps, such as mercury vapor lamps, metal halide (MH) lamps, ceramic MH lamps, sodium vapor lamps, and Xenon short-arc lamps. However, conventional phase control dimmers, such as a triac-based dimmer, that are designed for use with resistive loads, such as incandescent light bulbs, often do not perform well when supplying a raw, phase modulated signal to a reactive load, such as a switching power converter. Ballasts for many discharge lamps are not compatible with phase control dimmers. Many discharge lighting systems receive dimming information from a dimmer that provides a dedicated dimming signal. The dedicated dimming signal provides dimming information that is separate from power signals.
FIG. 1 depicts a power/lighting system 100 that receives dimming information via a dedicated dimming signal and, thus, avoids the problems of receiving dimming information via a phase-control dimmer Dimmer 102 provides lamp ballast 104 with a dedicated dimming signal in the form of dimming voltage signal DV. Dimmer 102 provides a reliable dimming signal DV. Dimmer 102 passes the AC input voltage VIN from AC voltage source 106 to lamp ballast 104. Input voltage VIN is, for example, a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe. Lamp ballast 104 provides a lamp voltage VLAMP to drive discharge lamp 108. The value of the lamp voltage VLAMP depends on the value of dimming voltage signal DV.
FIG. 2 depicts a light output graph 400 representing a graphical dimming-intensity function 202 between values of the dimming voltage DV and the percentage light intensity level of discharge lamp 108. The dimming voltage DV ranges from 0-10V, and the light intensity level percentage of discharge lamp 108 ranges from 10-100%. The dimming-intensity function 202 indicates that lamp ballast 104 saturates when the dimming voltage DV equals 1V and 9V. Between dimming voltage DV values of 0-1V, lamp ballast 104 drives the discharge lamp 106 to 10% intensity. Between dimming voltage DV values of 9-10V, lamp ballast 104 drives the discharge lamp 106 to 100% intensity, i.e. full “ON”. The dimming-intensity function 202 is linear between dimming voltage DV values of 1-9V with intensity of lamp 106 varying from 10-100%.
Phase control dimmers are ubiquitous but do not work well with reactive loads, such as lamp ballast 104. Thus, lamp ballast 104 does not interface with existing phase control dimmer installations. Thus, for lighting systems having an existing phase control dimmer, the phase control dimmer is replaced or bypassed to facilitate use of dimmer 102. Replacing or bypassing phase controlled dimmer adds additional cost to the installation of dimmer 102. Additionally, lamp ballast 104 does not provide a full-range of dimming for lamp 106.